1. Field of the Invention
This invention relates to a gear shift control mechanism for a multiple speed transmission having several shift rods which move axially to produce changes in the ratio of the input speed to the output speed. More particularly, the invention relates to an articulated shift lever for moving any one of the shift rods and an interlock for preventing the unselected shift rods from moving.
2. Description of the Prior Art
Multiple speed manual transmissions, particularly those having more than three forward speed ratios and one reverse drive ratio require a shift mechanism capable of effecting all of the required shifts with a manual shift pattern that is easy for the vehicle operator to follow. A transmission of this type generally has multiple shift rails mounted slideably on the transmission casing and carrying shift forks, which move synchronizer clutches to driveably connect a gear element of the selected gear ratio to the shaft on which it is journalled, usually either the countershaft or the output shaft. In transmissions of this type, the gear shift lever is usually mounted by a universal ball joint on an extension housing from which the shift rails extend forward to the synchronizers and shift forks. Generally, some form of interlock mechanism is provided that permits the selected shift rod to move as the shift lever is rotated and positively prevents movement of the shift rods other than the one selected by the vehicle operator. Usually the shift rails are each provided with detents that establish and maintain their positions among a neutral position, a forward position and a rearward position. Some means is required also to fix the path of travel of the gear shift lever and to maintain its position at a neutral position or a drive position. A detent, other than the shift rail detents, is usually provided to fix and maintain the position of the gear shift lever in the plane of the shift rails. Usually, there is a preferred neutral position to which the gear shift lever is continuously biased by a coiled spring.
In a top shift manual transmission, the shift rails are usually arranged directly below the universal ball joint connection that supports the gear shift lever on the transmission casing. Although the distance through which movement of the gear shift lever is transferred by the shift rails to the synchronizer sleeves and to the interlock mechanism is short in the top shift transmission, nevertheless the need for multiple detents on each of the shift rails and for some means to hold the gear shift lever engaged with the selected former shift fork is required.